Turbine engines which drive output shafts require, in view of the high speed of rotation of the turbine rotor, a reduction gearing to drive the output shaft at a reduced speed of rotation with a large torque. A typical application is a turboprop engine in which a gas turbine drives a propeller via a planetary gearing. Heretofore, for lubrication and abstraction of heat due to friction in the reduction gearing, a lubricating oil circuit therefor has been connected to the lubricating oil system of the gas turbine.
A new direction in the development of aircraft engine construction is represented by the propfan turbine engine in which one or two propfan rotors are connected to the driving gas turbine by a reduction gearing. For such propfan engines, the power transmitted is substantially greater than that of the most powerful turboprop engines.
Because of the amount of heat which is thereby produced in the reduction gearing and the increase in the turbine temperatures, the common lubricating oil system for the gas turbine and the reduction gearing has serious disadvantages. Accordingly, in view of the considerable amount of heat to be removed, a lubricating oil system which is more efficient than the traditional construction is required. A sufficiently dimensioned oil cooler arranged outside the engine requires long oil lines, as a result of which considerable frictional losses occur due to the large flow of lubricant. Furthermore, if the assembly consisting of the propfan rotors and the reduction gearing must be separated from the gas turbine, for example, for repair purposes, the oil lines must be interrupted which makes for substantial difficulty.